This application claims priority under 35 U.S.C. xc2xa7xc2xa7119 and/or 365 to 99 113 557.5 filed in Europe on Jul. 6, 1999; the entire content of which is hereby incorporated by reference.
The invention relates to an apparatus for measuring light that is emitted, remitted, or transmitted from a measuring object.
The so-called color management, i.e. the mutual tuning of all color capable computer peripheral devices (monitor, scanner, printer etc.) as well as the communication of reliable color values gains an increasingly great importance in the course of the continuous further distribution of color capable computer peripherals.
The creation of manufacturer specific device profiles or the creation of device profiles that correspond to a standard (e.g. ICC) is a central point of the color management. These device profiles allow for the conversion of device specific color values to device independent color values and hence into generally valid color values. The creation of device profiles is based on the characterization of the colorimetric properties of the input and output devices, such as color printer and scanner. This requires the colorimetric evaluation of color test cards (so-called test charts), such as described in the ISO standard IT8. One such test chart is composed of several hundreds of test fields. With the available portable measuring devices, the manual measuring of all test fields of a test chart requires a lot of work and time. This is due to the required precise manual positioning of the measuring device on the measuring field and the measurement time per color field which can last from one to several seconds. Even though the measuring of a test chart can be automated using a computer controlled XY-shifting table, it can be accelerated only insignificantly. Furthermore, such a XY-shifting table is very expensive.
The characterization and calibration of monitors is carried out by means of a direct measurement of the light emitted from the monitor. In doing so, the measuring device is commonly fastened to the screen of the monitor by means of a suction cup, for example.
The following basic requirements on a measuring device for color management can be derived from the steps described: the measuring device must have a flexible measuring geometry for the characterization of the different input and output devices (emission and remission) as well as a simple and efficient capacity for reading in one-dimensional and two-dimensional color test cards.
Existing color management solutions require several different measuring devices and apparatuses and are usually relatively expensive. The high purchase price of the measuring devices in comparison to peripheral devices restricts the use of color management to high end applications. Existing low cost color measuring devices require too much work for the creation of device profiles and thus have only a limited suitability for this application.
A characteristic feature of existing portable color measuring devices is a classical serial interface through which the device-internal and computer-based controller can communicate with a connected external computer. Communication means amongst other things, that measuring processes can be initiated and controlled by the external computer on one hand, and on the other hand the thus obtained measurement data transferred to the external computer, for example for further processing. The communication is controlled by corresponding software which is permanently stored in the color measuring device and loaded into the external computer when needed. Furthermore, data (e.g. measurement parameters) and if necessary specific software can be loaded from the external computer into the internal computer of the measuring device. Finally it is possible to manually trigger measuring processes at the measuring device itself.
Typical representatives of existing measuring devices that are designed to be portable are the xe2x80x9cColortronxe2x80x9d (U.S. Pat. No. 5,684,582), the disclosure of which is hereby incorporated by reference in its entirety, the xe2x80x9cDigital Swatchbookxe2x80x9d of the X-Rite company, and the xe2x80x9cSpectrolinoxe2x80x9d of the applicant. As a low cost device, the xe2x80x9cColormouse tooxe2x80x9d of the ColorSavvy company is mentioned.
The mentioned devices are different from each other by the type of their spectral analyzers. The xe2x80x9cSwatchbookxe2x80x9d is based on a greater number of narrow-band interference filters which are installed on a rotatable disk that is arranged in the path of the beam. This concept is not suitable for the measurement of narrow emission lines of CRT monitors because of the coarse wavelength resolution.
The xe2x80x9cColortronxe2x80x9d is based on a classical lattice monochromator combined with a receiver diode. This architecture evaluates the different wavelengths in a chronologically sequential manner. This leads to long measuring times during remission measurements. When performing emission measurements on the monitor, the measurement times are impractically long.
The spectral separation in the xe2x80x9cColormouse tooxe2x80x9d device is achieved through illumination by using different light emitting diodes (LED). The low illumination power of the LED combined with sequential measurements at different wavelengths leads to long measuring times. This measurement principle can inherently not be used for wavelength selective emission measurements.
The xe2x80x9cSpectrolinoxe2x80x9d of the applicant is based on a conventional diode array spectrometer which allows for short measuring times based on the simultaneous measurement of all wavelengths and can be used for emission measurements as well as remission measurements. Presently commonly used manufacturing technologies for diode array spectral modules cause relatively high costs and hence are unsuitable for a low cost device.
Today, the measurement off a complete test chart is carried out using time intensive manual performances of individual measurements which are carried out line-by-line using a device exclusively specialized for this application (e.g. DTP 41 by X-Rite) or fully automatic using a measuring device that is mounted on a computer controlled XY-table (e.g. Spectrolino-Spectroscan by the applicant). xe2x80x9cScanningxe2x80x9d color measuring devices that are mounted on a computer controlled measuring table are already mostly known in the printing industry and are described, for example, in EP-A 0064024, the disclosure of which is hereby incorporated by reference in its entirety.
A manually moved xe2x80x9cscanningxe2x80x9d portable measuring device is the subject of DE-A 197 16 066, the disclosure of which is hereby incorporated by reference in its entirety. The device described therein is moved parallel to its longitudinal edge during use, which is not optimal from an ergonomic point of view. It evaluates the received data for the measuring field recognition using the computer available in the detector. This requires the use of an extremely efficient small computer in the measuring device because of the high measuring speed. This concept can not be used in a low cost device.
It is an object of the present invention to improve a measuring apparatus of this type such that the constructive and conceptional prerequisites are created for a portable measuring device which is extremely affordable to produce and with which all necessary measurements for a complete color management process can be carried out in an efficient and precise manner. The measuring apparatus can perform approximately 100 measurements per second in a continuous measuring mode which allows for the automatic recording of several color fields through a manual pass across the color fields using the detector of the apparatus. In addition to its capability of being produced in an affordable manner, the measuring apparatus can be designed in a small and manageable manner, can be user friendly and not require maintenance, and thus can be generally available to a wide range of users.
In accordance with an embodiment of the invention the bidirectional interface is designed as a USB interface or fire wire interface which provides the technical requirements for a fundamentally different type of architecture (conception) of the measuring apparatus. This architecture reduces the required computing resources in the measuring apparatus to an absolute minimum and thus provides for a particularly affordable production of the apparatus. This reduction is achieved in accordance with a further embodiment of the invention by consequently swapping the digital data analysis into the connected host computer. The measuring apparatus itself only serves for the acquisition of raw data and their digitization, which massively reduces the production costs. The analysis of the data is carried out in the connected host computer making optimal use of resources (computer speed, storage capacity etc.) available in today""s personal computers. These resources are several times larger than the resources of the computers typically used in portable measuring devices. They allow for a real-time analysis of the raw data using more sophisticated algorithms than would be possible in portable measuring devices (at justifiable cost). The swapping of the data analysis into the external host computer further allows that the measuring apparatus, regardless of its relatively low computer resources, can be designed such that it can carry out approximately 100 measurements per second in a continuous measuring mode. This speed allows for an automatic capture of several color fields through a manual passing across the color fields using the detector of the measuring apparatus.
Because of the transfer of all raw data at a desired high measuring speed in the xe2x80x9cscanningxe2x80x9d mode, the architecture of the measuring apparatus in accordance with the invention requires a significantly higher band width for the data interface than the one provided in conventional devices commonly using a serial interface. Thus, the measuring apparatus in accordance with the invention uses a USB or Fire Wire (IEEE 1394) interface for the transfer of data from and to the external host computer.
The measuring apparatus in accordance with another important aspect of the invention is designed such that it can be supplied with energy through the interface (USB or Fire Wire) so that it will not need an additional (external) power supply which allows for a further reduction in costs.
The short measuring periods in remission measurements required for the scanning mode require a high intensity of illumination at a stable color temperature and intensity. These conditions can be fulfilled in a known manner using a precision incandescent lamp having an electrical power of at least 1.5 Watt and special control electronics.
When the incandescent lamp is turned on, significantly more power needs to be applied than is needed in the following stationary mode. This causes the following problem when using a USB interface: the USB standard allows in a xe2x80x9cHigh Power Devicexe2x80x9d a maximum electrical power consumption of 2.375 W. This is sufficient for the power supply of the internal computer and the stationary mode of the lamp, but during the turn-on phase of the lamp it is much too little. This problem is solved in accordance with a further aspect of the invention in that the measuring apparatus is equipped with an energy storage device, which is charged before the lamp is started and then supplies the required additional electrical power before and until the stationary state is reached. Thus, the incandescent lamp can be dimensioned such that it can absorb the maximum available power and hence can fulfill the above mentioned requirements.
A further reduction in costs is possible when equipping the spectrometer module of the measuring apparatus with a special thermal drift compensation that allows for an affordable assembly of the spectrometer from plastic material using an injection molding procedure. A spectrometer with such a thermal drift compensation is for example described in applicant""s U.S. patent application Ser. No. 09/538,236 of Mar. 30, 2000 (corresponding to EP Patent Application No. 99106111.0 of Apr. 01, 1999).
For the measurement of colored lines in the scanning mode, the user needs an aid which eases the guidance of the measuring opening of the measuring device along the colored line. In accordance with a further aspect of the invention the detector of the measuring device is equipped with a tubular extension which is substantially shaped like a pipe connector. The tubular extension contains the measuring opening and can be mechanically interlocked with an elongated guide slot of a ruler-like shifting guide. The tubular extension forms so to speak a mechanical interface to the shifting guide. The guide slot of this shifting guide functions as an aperture and allows visual control of the positioning of the detector on the measurement line. In the interlocked condition, the measuring device is limitedly rotatable around its longitudinal axis (optical axis of the detector) relative to the shifting guide and can be shifted along its lateral axis along the guide. For doing so, the shifting guide is held with one hand and the measuring device is held with the other hand. The shifting guide itself has a stiff rotatably mounted shaft with two rollers arranged at the ends which exclusively allows the parallel shifting of the guide and thus eases the positioning of the guide during the measurement of a two-dimensional test chart.
In accordance with a further advantageous embodiment, the detector or measuring tube has at its bottom end a further mechanical interface, e.g. a bayonet connection, which allows that a device (e.g. a suction cup) for the fastening of the device can be fastened to the screen of a monitor. The measuring tube is exchangeable and can be replaced with another one, for example one that is provided with a diffuser platelet for the measurement of the spectral composition of the surrounding light in front of the measuring opening.
Thus, the measuring apparatus in accordance with the invention is a portable measuring device that can be manufactured in a cost efficient manner and with which all necessary measurements for a complete color management process can be carried out efficiently and precisely. It is designed such that it can perform approximately 100 measurements per second in a continuous measuring mode. This speed permits the automatic capture of several color fields by manually passing over the color fields using the detector of the device. The measuring device in accordance with the invention offers for the first time a complete low cost color management solution based on an individual compact measuring device, which can be produced in a cost efficient manner and fulfills all described requirements for an efficient use in the area of color management. Through the combination of sequential measurements that can be executed at a high speed and a simultaneous manual shift of the detector one obtains a scanning system which measures a whole row of color fields with one movement. In doing so, an automatic recognition of the color fields is achieved later through analysis of the continuously captured measurement values.